Why am I am seeing an error in Outlook when clicking on a link to multiple email addresses?

We use commas to separate multiple email addresses in links because that is what is recommended by the RFC and because a recent update to the Outlook app on iOS devices causes it to no longer recognize multiple email addresses in links separated by a semicolon.

Outlook for the desktop, however, behaves differently than the app for iOS. It has a setting that must be enabled to allow multiple email addresses to be separated by commas: File > Options > Mail > Send messages > "Commas can be used to separate multiple message recipients" option. This setting is enabled by default and should allow the links to work in most cases.

In some cases, you may see an error stating that Outlook does not recognize commas. We have seen this happen when you proceed through the steps to click the link and attempt to send the email in quick succession.

On the other hand, if the setting mentioned above is enabled, in the 5-10 seconds it would take to compose an email message, Outlook will automatically convert the commas to semicolons. This means that your recipients are not likely to encounter the above error message in Outlook if they are using the link to send a normal email message to the designated recipients.

Alternatively if you have structured the link where they would not be taking the time to compose a subject line or message (and thus giving Outlook the time to convert the commas to semicolons) such as for pre-populated RSVP responses, and if you have a large proportion of recipients viewing from Outlook on the desktop, then you may need to consider updating the link to use a single email address in order to avoid recipients seeing the error message. You may want to contact your IT department to request a shared or team email address be created for your purposes.